Contact lenses and intraocular lenses made from silicone-containing materials have been investigated for a number of years. Such materials can generally be subdivided into two major classes, namely hydrogels and non-hydrogels. Non-hydrogels do not absorb appreciable amounts of water, whereas hydrogels can absorb and retain water in an equilibrium state. Regardless of their water content, both non-hydrogel and hydrogel silicone medical devices tend to have relatively hydrophobic, non-wettable surfaces that have a high affinity for lipids. This problem is of particular concern with contact lenses.
Those skilled in the art have long recognized the need for modifying the surface of such silicone contact lenses so that they are compatible with the eye. It is known that increased hydrophilicity of the contact lens surface improves the wettability of the contact lenses. This in turn is associated with improved wear comfort of contact lenses. Additionally, the surface of the lens can affect the lens's susceptibility to deposition, particularly the deposition of proteins and lipids from the tear fluid during lens wear. Accumulated deposition can cause eye discomfort or even inflammation. In the case of extended wear lenses (i.e. lenses used without daily removal of the lens before sleep), the surface is especially important, since extended wear lens must be designed for high standards of comfort and biocompatibility over an extended period of time.
Silicone lenses have been subjected to plasma surface treatment to improve their surface properties, e.g., surfaces have been rendered more hydrophilic, deposit resistant, scratch-resistant, or otherwise modified. Examples of previously disclosed plasma surface treatments include subjecting contact lens surfaces to plasma comprising an inert gas or oxygen (see, for example, U.S. Pat. Nos. 4,055,378; 4,122,942; and 4,214,014); various hydrocarbon monomers (see, for example, U.S. Pat. No. 4,143,949); and combinations of oxidizing agents and hydrocarbons such as water and ethanol (see, for example, WO 95/04609 and U.S. Pat. No. 4,632,844). U.S. Pat. No. 4,312,575 to Peyman et al. discloses a process for providing a barrier coating on a silicone or polyurethane lens by subjecting the lens to an electrical glow discharge (plasma) process conducted by first subjecting the lens to a hydrocarbon atmosphere followed by subjecting the lens to oxygen during flow discharge, thereby increasing the hydrophilicity of the lens surface.
U.S. Pat. Nos. 4,168,112, 4,321,261 and 4,436,730, all issued to Ellis et al., disclose methods for treating a charged contact lens surface with an oppositely charged ionic polymer to form a polyelectrolyte complex on the lens surface that improves wettability. U.S. Pat. No. 4,287,175 to Katz discloses a method of wetting a contact lens that comprises inserting a water-soluble solid polymer into the cul-de-sac of the eye. The disclosed polymers include cellulose derivatives, acrylates and natural products such as gelatin, pectins and starch derivatives. U.S. Pat. No. 5,397,848 to Yang et al. discloses a method of incorporating hydrophilic constituents into silicone polymer materials for use in contact and intra-ocular lenses. U.S. Pat. Nos. 5,700,559 and 5,807,636, both to Sheu et al., discloses hydrophilic articles (for example, contact lenses) comprising a substrate, an ionic polymeric layer on the substrate and a disordered polyelectrolyte coating ionically bonded to the polymeric layer. U.S. Pat. No. 5,705,583 to Bowers et al. discloses biocompatible polymeric surface coatings. The polymeric surface coatings disclosed include coatings synthesized from monomers bearing a center of positive charge, including cationic and zwitterionic monomers. European Patent Application EP 0 963 761 A1 discloses biomedical devices with coating that are said to be stable, hydrophilic and antimicrobial, and which are formed using a coupling agent to bond a carboxyl-containing hydrophilic coating to the surface by ester or amide linkages.
Plasma treating operations are performed in large, batch process reactors. In one prior art method, contact lenses requiring surface treatment are dry-released from the anterior mold and edged polished, if necessary. The lenses are placed manually by a worker concave-side up into a transfer tray. The transfer tray contains a plurality of cylindrical cavities with flat bottoms and is typically made from white polystyrene having a matte finish. The lens diameter is typically smaller than the diameter of the cavity so that the lens is easily placed and retrieved from the tray. The lenses are taken to a different workstation for surface treatment. At the surface treatment station (e.g. using commercial Metroline Plasma Deposition Model Number 7100 Series Chamber), lenses are inverted onto a surface treatment tray such as the removable shelf supplied with the Metroline Plasma Chamber. The Metroline shelf has a plurality of small, spaced perforations located at predetermined intervals, each of the perforations having diameters substantially smaller than any one of the lenses. Each lens is placed on the shelf, concave-side down. The lenses are plasma reacted and inverted, e.g. using a manual method or using a semi-automated device such as an air knife as disclosed in U.S. Pat. No. 5,503,515 (Moorehead, assigned to Bausch & Lomb Incorporated). Unfortunately, it has been found that when lenses are initially inverted from the transfer tray onto the Metroline shelf, placement of the lenses is random with the individual lens not necessarily over a perforation as intended. If an individual lens is not situated over a perforation, the lens will not invert. Instead, a worker must use tweezers to turn the lens over. The other side of the lens is then subjected to a plasma reaction. The surface treatment requires two cycles of plasma reaction. The lenses are then picked up by a worker using tweezers and transferred for other processing such as extraction. The worker is integral to this whole process, especially in making sure all the lenses invert over the air knife and transferring the surface treated lenses for extraction.
Others have shown apparatus for individually handling lens. For example, U.S. Pat. Nos. 5,969,793 and 6,502,879 show apparatus for removing individual lenses from molds and for transferring the lenses to other process apparatus. It is also known that a lens may have its edge polished while the lens is supported on a spindle and the edge polishing tool is moved in relation to the spindle. See U.S. Pat. App. Pub. 2002/0115389 published Aug. 22, 2002.
Thus, it is desired to provide a plasma process for treating the surfaces of silicone hydrogel contact lens with an optically clear, hydrophilic surface film that will not only exhibit improved wettability, but which will generally allow the use of a silicone hydrogel contact lens in the human eye for extended period of time. There is also an unmet need for a more efficient process that plasma treats lenses one at a time in sequence with the edge polishing step. In the case of a silicone hydrogel lens for extended wear, it would be desirable to provide a contact lens with a surface that is also highly permeable to oxygen and water. Such a surface treated lens would be comfortable to wear in actual use and would allow for the extended wear of the lens without irritation or other adverse effects to the cornea. It would be desirable to manufacture such a surface treated lens without the need for an oxidation step such as plasma treatment or corona discharge treatment.